This invention relates to the fracturing of subterranean formations and more particularly to a method for forming fractures in a plurality of vertically disposed hydrocarbon-bearing formations communicating with a well equipped with a casing penetrating a subterranean earth formation.
Hydraulic fracturing techniques have been extensively used for treating subterranean hydrocarbon-bearing formations. Generally, perforations or slots are formed in well casing adjacent a formation to be fractured. Hydraulic fluid is then pumped down the well through the perforations and into contact with the formation. Hydraulic pressure is applied in a sufficient amount to fracture the formation and thereafter fluid is pumped into the fracture to propogate the fracture into the formation. It is generally accepted that, at depth, vertical fractures are formed in most formations when a sufficiently high hydrualic pressure is applied to fracture the formation. At shallower depths it is recognized that horizontal fractures may be formed in formations by applying a pressure greater than the overburden pressure.
In U.S. Pat. No. 3,028,914 to Flickinger there is described a method of producing multiple fractures from a cased well. A first fracture is made and extended into a formation. The same formation or another formation penetrated by the same well may then be fractured by plugging the mouth of the first fracture, making a number of perforations concentrated within a short section in the casing and then injecting fracturing liquid into the well and initiating a second fracture at the elevation of the second set of perforations.
In U.S. Pat. No. 3,547,198 to Slusser, there is described a method of forming two vertically disposed fractures which communicate with a cased well penetrating a subterranean formation having a preferred fracture orientation. Openings are formed through the well on opposite sides of the casing located such that they lie in a vertical plane which extends transversely of the fracture orientation. Hydraulic pressure is then applied through the openings to form a fracture at the openings on one side of the well. The openings are then temporarily sealed and hydraulic pressure is applied to form a fracture at the openings on the other side of the well. Thus, two fractures are formed adjacent opposite sides of the well and are propagated into the formation approximately parallel one to the other.
It is therefore, well known to provide temporary sealing means to well casing adjacent a first fractured earth formation so that subsequent fracturing can be carried out at other elevations within a well. Thus, by successive fracturing and sealing operations, fractures can be formed in a plurality of earth formations within a given well.